Published: October 2014

In last
month’s bulletin1, I discussed the case of a young child whose
unerupted maxillary permanent canines were in an ectopic location which appeared
certain to result in their bilateral impaction. Orthodontic correction of the
orientation of the roots of the adjacent incisors was used as a preventive
measure to alter the relationship between the canines and the lateral incisor
apices. This alteration in the environment encouraged the canine teeth to adopt
a normal path of eruption.

In the
present bulletin, a case of bilateral canine impaction is presented in which
the exact opposite situation occurred. Here, an orthodontic appliance was used with
the intention of creating space for the canines. Instead however, the roots of
the lateral incisors were unintentionally moved in the opposite direction, thereby
complicating the impaction of both canines. On the one side, the canine had
become obstructed by the incisor root, while on the other, the canine and the
incisor had become transposed.

The female
patient was 17 years of age at her only visit to my office, on July 4 2014, on
the recommendation of the treating orthodontist and oral surgeon. The patient
had been in orthodontic treatment with the orthodontist
for the past 4 years.

Her
medical/surgical history revealed a background of benign lymphatic malformation
of the upper lip, which had been treated surgically in Boston several years
earlier. At examination, her appearance was good, with some relatively minor asymmetric
residual swelling of the upper lip. There was a related loss of height of the
labial sulcus in the upper jaw, presumably associated with adhesions and scarring
of the oral mucosa from the surgical procedures.

Fig. 1a-e. intraoral views of the of the dentition after
space had been re-opened in the canine region to accommodate the impacted
canines. The right second premolar bracket had debonded. The pigtail stainless
steel ligature can be seen attached by a traction elastic tie to the
premolarbracket.

Fig. 1d, e. A front view, with the teeth apart and an
occlusal view, showing space opening for the canines and the widened premolar area.

The malocclusion
was defined as Angle’s class 1 bimaxillary protrusion, with large teeth and a
mild degree of lower incisor crowding (Fig. 1a-e). The molar relation was
normal. A fixed multibracketed edgewise appliance was present in the upper jaw,
which had brought about alignment of the teeth and the creation of space in both
canine regions to accommodate the two unerupted maxillary permanent canines. A full
thickness rectangular NiTi archwire was in place. However, there was also
uncontrolled widening of the premolar area into a buccal crossbite. The
maxillary canines were impacted although only the left one had been surgically
exposed 2 years earlier, followed by the application of traction in the
direction of the bracket on the first premolar.The patient’s complaint was that there appeared to be little or no
progress in the treatment of the left side, while nothing had been done about
the right canine.

Fig. 2. The 2006 panoramic radiograph of the early mixed
dentition and showing the maxillary canines very high up and in close relation
with the incomplete root apices of the lateral incisors. The unerupted right
first premolar is tipped distally and the early development of the root has
encroached mesially on the eruption path of the canine.

The patient
produced a series of 4 panoramic radiographs starting from 2006 and 2 separate
CBCT imaging records taken in 2010 and 2014, respectively. The panoramic view
from June 2006 was taken when the patient was 9 years old and it showed that
all her permanent teeth were developing with the exception of the third molars
(Fig.2). Both permanent canines could be seen high in the maxilla and appeared
to be following a more mesial path than normal, with the left one in the
process of mesially by-passing the lateral incisor. The right canine was
closely related to the wide open apex of the lateral incisor, while the adjacent
and unerupted right first premolar had a mild but abnormal distal crown
angulation. A degree of crowding was clearly visible on the film, in the
anterior regions of both jaws.

Fig.3. The 2008 panoramic view of the late mixed
dentition. The two impacted canines have acquired enlarged follicles and have
reached the distal of the central incisor roots, by-passing the lateral incisors.

The December
2008 panoramic view showed both canines still very high up, with the left one
showing a greater degree of vertical development than the right one but, at
this point, both were in close proximity of the distal side of the roots of the
central incisors and both displayed enlarged follicles (Fig. 3). Orthodontic
treatment had not commenced at that time.

Fig. 4. The May 2013 film shows how the bonded appliance
has tipped the roots of the lateral incisors distally, creating a partial
transposition with the mesiallytipped
canines. An attachment is present on the unerupted left canine and a steel ligature
can be seen leading from it directly towards thefirst premolar.

The May 2013
panoramic film showed the orthodontic appliance in place (Fig. 4). Space had
been achieved at the occlusal level between the crowns of the lateral incisor
and first premolar on each side. However and presumably due to misjudged
bracket placement on the lateral incisors, the roots of these teeth had been
distally tipped, where they were in close proximity to the roots of the first
premolars. The right unerupted canine had not been exposed and its location was
largely unchanged, although its relationship to the distally moved apex of the
lateral incisor had now been severely worsened. The left canine had been surgically
exposed and an attachment bonded. The subsequent traction, using a steel
ligature to the premolar, had brought the tooth down to a minimal degree, but
it could now be seen to be wedged between central and lateral incisor.

From the
panoramic film taken a half year later, in November 2013, there appeared to have
been little significant change in the positions of either impacted canine, which
is not surprising since the right canine was still untreated and the left was being
continuously drawn to the premolar region while being trapped between lateral
and central incisor (Fig. 5).

A
pre-treatment cone beam CT had been taken in June 2010 and comprised only a
single printed page of transaxial cuts, with no labeled grid guide to show
where these cuts were made and to which side of the patient they referred. No
other print-outs from this CBCT scan were available and the radiology institute
no longer had these records in its archive – a serious display of disregard for
the standard of care, on the part of the institute.

Fig. 6a. The graded section of the CBCT version of the
panoramic view of the untreated right side. Parts b, c & d are transaxial
“slices” through the ridge at cuts 29, 17 and 8 respectively on the grid of the
panoramic view and reoriented to comply with it. Parts e, f & g are axial
cuts to show how the apex-crown orientation of the canine straddles the
alveolar ridge from lingual to labial, between the roots of the lateral and
central incisors.

A second CBCT
was taken in February 2014 and it illustrated the impacted right canine with no
apparent pathology and with a good root. The tooth was oriented labio-lingually
across the dental arch, at the level of the apical third of the roots of the
other teeth, with a strong mesial tip and its root apex palatal and crown
labial to the lateral incisor. The mesial aspect was
located in the lateral aspect of the root apex of the central incisor, while
the extreme tip of the crown was on the labial side of the alveolar ridge, unerupted and high
in the sulcus. Its relationship to the lateral incisor had been reversed and a
transposition had been created by the iatrogenic, appliance-generated, distal
displacement of the root of the lateral incisor (Fig. 6).

Fig 7a. The graded section of the CBCT version of the
panoramic view of the treated side.Parts
c, e and f show the contact of the crown of the canine with the root of the
lateral incisor. The root of this lateral incisor is being labially torqued by
the rectangular archwire and directly iimpinging against the canine. This is overwhelmingthe canine from responding to the distal traction applied to it. The
axial cut in part d shows the right canine root to be located in the medial
bony partition between maxillary sinus and nasal cavity.

As we have
already noted, the root apices of both lateral incisors had been distally displaced
by the orthodontic appliance. However, their roots were also lingually
displaced to a marked degree, no doubt due to the influence of the labial
locations of the unerupted canines. With a full thickness rectangular NiTi
archwire ligated into the teeth of the maxillary dentition, there was a strong
labial torqueing moment on both lateral incisors. This had obviously brought
about a clash between the root end of the left lateral incisor and the canine, which
was the most likely cause of lack of progress in moving the unerupted left
canine distally (Fig. 7). The same torqueing moment acting on the right lateral incisor
was similarly a contributory cause preventing the right canine from autonomously
migrating in a downward direction.

To
complicate matters still further, the axial (horizontal) cuts of the CBCT show
the root apex of the right canine to lie on the medial aspect of the maxillary
sinus, on the partition wall between the sinus and the nasal cavity. This effectively
means that the tooth will require much labial roots torque, following its
relocation in the dental arch and, drawing the tooth to the lateral incisor
location and accepting the transposition, would appear to be an acceptable
remedy for the problem.

Attempting
to move the right canine distally around the lateral incisor to its place in
the arch is an option, but treatment would be considerably longer and the
prognosis of each of the teeth consequently poorer.

One further factor
which often goes unnoticed in these situations is the orientation of the
premolar teeth.2, 3 On both sides of the jaw in this case, the
premolar roots were tipped mesially and in close proximity to the roots of the
canines, which can unquestionably contribute to the resistance to movement of
the teeth.

Recommendations for treatment:

1.Relocate the brackets on the premolars to over-upright
the roots of these teeth distally and rotate the tooth in a mesio-lingual
rotation, thereby to distance the palatal root from contact with the root of
the mesially angulated canines. 2, 3

2.Surgical exposure of the right canine, from high on
the labial side to avoid the resorbing area of the central incisor and traction
using an auxiliary labially-directed ballista-type spring, initially.

3.Redirect the twisted steel ligature on the left canine
to permit labial traction

4.Relocate the bracket on the left lateral incisor for
mesial uprighting on a round cross-section archwire.The use of a rectangular archwire is strongly
contraindicated.

5.Use a labially-directed auxiliary ballista-type springs,
piggy-back style, to move the left canine crown labially around the root of the
incisor, before re-applying distal traction once the tooth is clear.

On the right
side, as noted above, one may feel justified in accepting the iatrogenically
created transposition and align the canine and lateral incisor in their
reversed order, particularly since the patient has already experienced 4 years
of orthodontic treatment. For this option, it will be necessary to move the
right lateral incisor distally into the canine location, expose the right
canine and draw it labially, erupting it inferiorly in the line of the arch in
the place of the lateral incisor.

Nevertheless,
a careful study of the inter-relations between the teeth on the right side
should lead the reader to conclude that the lateral incisor root is both
inferior to and lingual to the canine. This would indicate that a mesial
re-uprighting of the incisor root and a distal and inferior movement of the
crown of the canine are possible without their roots colliding, provided no
labial incisor root torque is performed until the transposition has been fully resolved.
This means that a round base archwire, rather than a rectangular base archwire,
should be used with light wire springs and auxiliaries to effect individual
movements.Thus, alignment of these
teeth in their correct order is possible. It will take much additional time
but, since the esthetic zone is the area affected, it may be the preferred line
of treatment.